PM: add /sys/power documentation to Documentation/ABI

The file sysfs-power that documents the interface in the /sys/power/ directory
is added to Documentation/ABI/testing.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 88 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-power b/Documentation/ABI/testing/sysfs-power
new file mode 100644
index 000000000000..d882f8093871
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-power
@@ -0,0 +1,88 @@
+What:           /sys/power/
+Date:           August 2006
+Contact:        Rafael J. Wysocki <rjw@sisk.pl>
+Description:
+                The /sys/power directory will contain files that will
+                provide a unified interface to the power management
+                subsystem.
+
+What:           /sys/power/state
+Date:           August 2006
+Contact:        Rafael J. Wysocki <rjw@sisk.pl>
+Description:
+                The /sys/power/state file controls the system power state.
+                Reading from this file returns what states are supported,
+                which is hard-coded to 'standby' (Power-On Suspend), 'mem'
+                (Suspend-to-RAM), and 'disk' (Suspend-to-Disk).
+
+                Writing to this file one of these strings causes the system to
+                transition into that state. Please see the file
+                Documentation/power/states.txt for a description of each of
+                these states.
+
+What:           /sys/power/disk
+Date:           August 2006
+Contact:        Rafael J. Wysocki <rjw@sisk.pl>
+Description:
+                The /sys/power/disk file controls the operating mode of the
+                suspend-to-disk mechanism.  Reading from this file returns
+                the name of the method by which the system will be put to
+                sleep on the next suspend.  There are four methods supported:
+                'firmware' - means that the memory image will be saved to disk
+                by some firmware, in which case we also assume that the
+                firmware will handle the system suspend.
+                'platform' - the memory image will be saved by the kernel and
+                the system will be put to sleep by the platform driver (e.g.
+                ACPI or other PM registers).
+                'shutdown' - the memory image will be saved by the kernel and
+                the system will be powered off.
+                'reboot' - the memory image will be saved by the kernel and
+                the system will be rebooted.
+
+                The suspend-to-disk method may be chosen by writing to this
+                file one of the accepted strings:
+
+                'firmware'
+                'platform'
+                'shutdown'
+                'reboot'
+
+                It will only change to 'firmware' or 'platform' if the system
+                supports that.
+
+What:           /sys/power/image_size
+Date:           August 2006
+Contact:        Rafael J. Wysocki <rjw@sisk.pl>
+Description:
+                The /sys/power/image_size file controls the size of the image
+                created by the suspend-to-disk mechanism.  It can be written a
+                string representing a non-negative integer that will be used
+                as an upper limit of the image size, in bytes.  The kernel's
+                suspend-to-disk code will do its best to ensure the image size
+                will not exceed this number.  However, if it turns out to be
+                impossible, the kernel will try to suspend anyway using the
+                smallest image possible.  In particular, if "0" is written to
+                this file, the suspend image will be as small as possible.
+
+                Reading from this file will display the current image size
+                limit, which is set to 500 MB by default.
+
+What:           /sys/power/pm_trace
+Date:           August 2006
+Contact:        Rafael J. Wysocki <rjw@sisk.pl>
+Description:
+                The /sys/power/pm_trace file controls the code which saves the
+                last PM event point in the RTC across reboots, so that you can
+                debug a machine that just hangs during suspend (or more
+                commonly, during resume).  Namely, the RTC is only used to save
+                the last PM event point if this file contains '1'.  Initially
+                it contains '0' which may be changed to '1' by writing a
+                string representing a nonzero integer into it.
+
+                To use this debugging feature you should attempt to suspend
+                the machine, then reboot it and run
+
+                dmesg -s 1000000 | grep 'hash matches'
+
+                CAUTION: Using it will cause your machine's real-time (CMOS)
+                clock to be set to a random invalid time after a resume.